1. Field of the Invention
The present invention generally relates to a planar light source apparatus applicable to a liquid crystal backlight module.
2. Description of Related Art
Light source apparatuses are widely used in the daily life. The conventional light source apparatuses such as light bulbs produce a visible light source by passing a current through filaments to heat up. The light bulbs are generally spot light sources. Later, the tube light source is developed. After a long term development and modification, planar light source devices are put forth and widely used in planar displays.
Light source may be produced through many mechanisms. FIG. 1 is a schematic cross-sectional view showing a conventional planar light source apparatus mechanism. Referring to FIG. 1, the light emitting mechanism is realized by connecting two electrode structures 100 and 102 to a power supply 106 to generate an electric field under an operating voltage, and then ionizing the gas 104 though gas discharging (also referred to as plasma discharging) to generate electrons 110. The electrons 110 is accelerated by the electric field to hit the corresponding red, green, and blue fluorescent layers 108a, 108b, and 108c on the electrode structure 102. The visible lights 112 are then generated and emitted through the fluorescent layer. Herein, the electrode structure 100 is a light-emitting surface, and generally is made of a light transmissive material constituted by a glass substrate and an indium-tin-oxide (ITO) transparent conductive layer.
Another light source generating mechanism is the field emission mechanism as shown in FIG. 2. FIG. 2 is a schematic cross-sectional view showing another conventional planar light source apparatus mechanism. The conventional planar light source apparatus includes a glass substrate 120, a cathode structure layer 122, a plurality of conical conductors 124, a gate layer 126, an anode structure layer 128, and a fluorescent layer 130. The cathode structure layer 122 is disposed on the glass substrate 120. A plurality of conical conductors 124 is disposed on the cathode structure layer 122. A gate layer 126 is disposed on the conical conductor 124. A plurality of holes corresponding to the conical conductors 124 is formed in the gate layer 126. The anode structure layer 128 has a transparent anode layer disposed on a glass substrate. Moreover, the fluorescent layer 130 is disposed on the anode structure layer 128. The electrons 132 escape from the tip of the conical conductor 124 under the high electric field between the cathode and the anode and are accelerated by the electric field to hit the fluorescent layer 130 so as to emit visible lights.
The above two conventional light-emitting mechanisms have respective advantages and disadvantages. The gas discharge manner is easy and the structure is simple, but the plasma is generated in the process, thus consuming energy. The field emission light source is a kind of cold light source and has a similar principle like the cathode ray tube (CRT) wherein the electrons escape from the cathode under the high electric field between the cathode and the anode and then hit the phosphors coated on the anode to emit light. The field emission light source is advantageous in high brightness and power saving, and is easy to be made into a planar structure. However, the field emission light source has the disadvantages that the emission material needs a spindle structure or carbon nanotube to grow or be uniformly coated on the cathode. This planar fluorescent lamp must use a support to separate the cathode and the anode, and the vertical distance between the cathode and the anode must be adjusted carefully. Since the tolerance is small, the cost of the structure design and the yield must be taken into account in mass application, and the uniformity of the overall light brightness is difficult to control. Moreover, the vacuum packaging is also a problem.